The present invention relates to an apparatus for detecting the availability of a workpiece carrier in a predetermined track portion of a workpiece carrier transportation path, which includes a housing, a slider which is displaceably guided in the housing and displaced directly or indirectly by the workpiece carrier, and at least one proximity switch releasable by the slider.
Such apparatuses are known in the prior art and identified as “rockers”. They can be arranged for example laterally on the workpiece carrier transporting path for detecting the transitional movement of a workpiece carrier (FIG. 1). The workpiece carrier is brought in engagement with the slider of the rocker and deviates it in a direction which is substantially orthogonal to the movement direction of the workpiece carrier. The displacement movement of the slider can be detected by a proximity switch. The output signal of the proximity switch can be used to control further steps, for example a processing step to be started on a workpiece arranged on the workpiece carrier.
It is however also possible to allow running of the workpiece carrier head-on against the rocker so that the slider is displaced by the workpiece carrier substantially in its movement direction (FIG. 2). In this case the output signal of the proximity switch can set in operation for example a pushing device or a transferring device which transfers the workpiece carrier from the current transporting path to the next following transporting path.
Conventionally, the slider in the known rockers is displaceably guided in the housing by means of cooperating wall surfaces of the slider and the housing.
The disadvantage of the known constructions of such rockers include first of all the fact that during engagement of the workpiece carrier and the slider a tilting of the slider, and if worse come to worse, a turning and clamping of the slider in the housing can occur. The switching conditions of the proximity switch released by the slider can not be reproduced in this case with the required accuracy, in particular a switching delay can occur.